A photodiode using compound semiconductors is known as a photodiode with a high spectral sensitivity characteristic in the near-infrared wavelength band (e.g., cf. Patent Literature 1). The photodiode described in Patent Literature 1 is provided with a first light receiving layer comprised of one of InGaAsN, InGaAsNSb, and InGaAsNP, and a second light receiving layer having an absorption edge at a longer wavelength than that of the first light receiving layer and comprised of a quantum well structure.